Method of measuring the temperature of sugar-bearing materials



-BEARING MATERIALS June 29, 1954 c. A. OLCOTT METHOD OF MEASURING THE TEMPERATURE OF SUGAR Filed Aug. 21

INVENTOR. Oman; 4. 0Lcorr Patented June 29, 1954 UNITED STATES PATENT OFFICE METHOD OF MEASURING THE TEMPERA- TUBE F SUGAR-BEARING MATERIALS Charles A. Olcott, West Milford, N. J.

Application August 21, 1950, Serial No. 180,587

2 Claims. 1

This invention relates to the temperature conditioning of materials and more particularly to methods of temperature-conditioning sugar-bearing materials.

It is an object of this invention to provide improved processes for heating or cooling sugarbearing materials.

It is very important in the art of sugar manufacture that the temperature to which massecuite in a IlllXlIlg tank is heated (usually by a rotating hollow coil containing hot fluid) prior to bein separated in the centrifugals should be carefully and accurately controlled. The reason for this is that massecuite which is too cold will not purge readily in the centrifugal machine, because low temperature adds to the viscosity of the molasses, and thus any temperature lower than that necessary results in an increase in the amount of molasses adhering to the crystal, which molasses will not be' removed by centrifugal force,- and which therefore will require more Water than would overwise be necessary for washing. This has the effect of causing losses of sugar due to ire-dissolvin by the excess of wash water. It is generally accepted that the viscosity of molasses doubles with every Q degree drop in temperature, and thus it will be readily seen that even a few degrees has the effect of substantially increasing the amount of molasses adhering to the sugar grains after centrifuging. Conversely, ifmassacuite is heated above the saturation temperature, the sugar crystals immediately begin to re-dissolve, and thus even a slight degree of over-heating might cause considerable loss of sugar. It is obviously desirable to heat the massecuite as closely as possible to saturation temperature in order to effectively separate the sugar crystals from the molasses.

lhe practice generally followed at the present time is to insert a bulb of a thermometer into the mixing tank or crystallizer containin the massecuite, and to judge the temperature of the massecuite by observing the temperature indicated by the thermometer attached to the bulb. Such a method of determining temperature is apt to be very inaccurate, since the thermometer bulb cannot be inserted within the sweep of the coil used to heat the massecuite, because to do so would result in the coil breaking the bulb. Therefore the bulb must be inserted into the massecuite outside of the sweep of the coil, and as this massecuite is not directly stirred, its temperature can be substantially difierent, and usually colder, than the temperature of the massecuite actually being stirred by the coil. The reason for this is that massecuite is a very poor conductor of heat, and furthermore there is a tendency for the massecuite and sugar crystals to accumulate around the bulb, forming a crust which further insulates the bulb from the bulk of the massecuite being stirred. Furthermore, the thermometer bulb is usually made of metal which can readily conduct the lower temperature of the air outside of the tank to the gas Within the bulb, and thus the thermometer bulb reflects not the temperature of the massecuite actually being heated and stirred, but produces a reading based on both the temperature of the unstirred portion of the massecuite and that of the air outside of the crystallizer. Thus the thenmometer bulb is very apt to indicate a temperature considerably lower than the actual temperature of the bulk of the massecuite, and if the stirring and heating action is continued until the thermometer indicates the saturation temperature of the massecuite, it is probable that the great bulk of the massecuite actually being heated and stirred is considerably above the saturation temperature, and this will result in the loss of sugar due to re-dissolving.

In order to eliminate this hazard, there is provided in accordance with the invention a process for determining Within close limits the temperature of the massecuite actually bein heated and stirred. In this process, a thermometer bulb is inserted in the piping either inside or outside the mixing tank, such as, for example, in the return pipe of the circulating system of the coil. After the hot water used for heating the massecuite in the mixer tank has been allowed to flow through the coil for a predetermined period taught by experience to be sufiicient to heat the massecuite to near the desired temperature, the valve in the circulatin system is closed and the hot water circulation shut oil. The coil, however, continues to rotate in the massecuite for a second predetermined period during which the hot water in the coil continues to exchange heat with the massecuite and the water in the coil comes to a temperature very close to that of the massecuite. At the end of this second period, the operator allows water to circulate again through the coil and thus causes water Which is now at the massecuite temperature to flow through the return line containing the thermometer bulb. The reading of the thermometer is a very close approximation of the actual temperature of the bulk ofthe massecuite stirred by the coil rather than the temperature of some small unstirred portion of the massecuite. In an alternative arrangement, the bulb of the thermometer may be placed inside the central portion of the coil or in any other suitable place in the water circulating system.

The invention will be more readily understood by referring to the following description taken in connection with the accompanyin drawing forming a part thereof, in which the single figure shows an arrangement for heating massecuite in a mixer tank and illustrates a process in accordance with the invention for accurately indicatin the temperature of the stirred portion of the massecuite.

Referring more specifically to the drawing, the

single figure shows a mixer tank It! for heating massecuite to be used in the manufacture of sugar. t is to be understood that after the massecuite in the tank III has been temperatureconditioned to the desired temperature, it is conducted to a centrifugal and there acted upon in wellknown manner. While the massecuite in the tank I I] can be either heated or cooled, and the temperature measuring process of the invention is applicable to either case, it will be described by way of example in connection with the case where the massecuite is to be raised in temperature. The source II of hot water preferably comprises a tank heated by any suitable means such as the coil I2. Steam or hot water is passed to the coil I2 through a valve i3 controlled by a thermostatic bulb I4. This bulb controls, in a well-known manner, the valve 53 to insure that the temperature of the water con tained in the tank II is maintained at a predetermined temperature, such as, for example, around 200 degrees F. Hot water at this temperature is drawn from the tank II through a conduit or pipe I5 by means of the pump IE5 and the water is driven by the pump through a pipe or conduit ll having a valve therein (which may be operated from a remote control station H, if desired) into the rotary heating means or coil It in the mixer tank l0. This coil I8 is in the form of a rotary stirrerand comprises, by way of example, a first pair of coil sections or branches I 9 adapted to rotate in the magma, a second pair of rotatable coil sections or branches 23, heat exchanger 2| comprising an outer pipe 22 and an inner pipe 23 coaxial therewith cooperating with the first pair of branches I3, and passages thereto and therebetween. The hot water from the source I I at a temperature above 190 degrees F. enters the inner pipe 23 through a hollow shaft 24 which is connected to the inner pipe 23 and which forms a supporting means for the outer pipe 22. The. other end of the pipe 22 has or is attached to a flanged member 2? which is bolted or otherwise secured to the flange 23 of the hollow shaft 29. The end of the inner tube 23 remote from the inlet end thereof is supported in a wall or diaphragm member 33. The member 38 seals one end of the pipe 23 and the annular space 34 between this pipe and the pipe 22. It can be, for example, a casting provided with a passage from the inner pipe 23 to passages leading to each of the coil branches I9, and passages or pipes 33 between the annular space 34 and a chamber 35 leading to the hollow shaft 29 which leads, in turn, to another hollow shaft 36. The latter shaft opens into a chamber 31' which has as parallel outlets the two coil sections or branches 20. The latter branches are in contact with the magma in the tank I0 and they terminate in a chamber leading to a hollow shaft 33. Thus Water flows successively through hollow shaft 24, pipe 23, coil branches I3, annular space 34, openings or passages 33, chamber 35, hollow shafts 29 and 36, chamber 3?, coil branches 20, and hollow shaft 39. All of these members are considered part of the coil. Ihe hollows shafts 24, 29, 36, and'39- are supported by suitable bearings and connections to and from these hollow shafts are made by means of rotary joints 43, M and 42 respectively. The hollow shaft 36 has. a flange 43 which is attached to the flanged member 44 which supports one end of a pipe 45 having a partition 46 and another partition at the other end thereof to seal oil the coil sections 20 from the central section of the pipe 55. The other end of the pipe 65 is sup-- ported from the hollow shaft 39. While the coil I8 described above (and which is more completely described and claimed in a copending application of C. A. Olcott, Ser. No. 575,595, filed February 1, 1945) is believed to be very eflicient and is preferred, it will be obvious that the invention is not limited to the use thereof as any other suitable rotating coil can be used instead. One such suitable coil section is disclosed in Patent 1,934,006 to W. A. Rotston.

The hollow shafts are rotated by a pulley 5 driven by any suitable source of power, such as the motor 5|. The hot water in the hollow shaft 39 of the rotary heating means or coil I8 is conducted to a thermostat device 52. The latter can be of the bellows type comprising a metal gas-filled thermostatic bellows which is adjusted by a manually operated wheel 54 passing through the chamber containing the bellows. A valve stem rod 55 is connected to a valve head in valve 58. The expansion and contraction of the bellows operates to raise and lower the valve head in the valve to regulate the volumetric flow of the water through the system.

When the valve head is raised out of engagement with its associated valve seat, water flows through the system by means of a pipe 58 connecting the chamber 59 of thermostat device 52 with valve 60. When the valve head in valve 50 is closed against its seat, the flow stops. From the valve 60 the water passes through a pipe 6| to the heater tank II where the temperature of the return water is once again brought up to above degrees F.

In a chamber 62 between the pipe 58 and the valve 60 is a thermostatic bulb 63 which is connected to any suitable temperature indicating device 64 by wires 65. This thermostatic bulb in this particular place in the system, that is, outside the mixing tank II] but within the circulating system used to heat it, makes possible the novel process of this invention.

The operation of the arrangement shown in the drawing will now be described, following which the detailed steps of the process of measuring the temperature of the massecuite will be set forth. Assume that the water in the heater tank I I is brought up to such a temperature that after it has passed through the pipes I5 and Il', the pump I5 and the hollow shaft 24 it is at least 190 degrees F. After passing through the inner pipe 23, the water is then passed through the two coil sections I 5 in parallel. By the heat exchange action between these coil sections and the massecuite or magma in the tank II) (as the coil sections are revolved by means of the pulley 50 and motor 5|), the temperature of the water in the coil sections I9 as it flows into the annular space 34 is decreased but the temperature of the massecuite or magma is raised because of theheat exchange action between these coil sections and the magma. As the water flows through the annular space 34, its temperature is raised (by the heat exchange action between the water in this space and the water in the pipe or tube 23) and in its reheated condition is passed into the coil sections through the parallel passages 33, the chamber 35, the hollow shafts 2e and 36 and the chamber 31. By the heat exchange action between the rotating coil sections at and the magma in the tank [0, the temperature of the water (as it flows into the hollow shaft 39) has been lowered to about 140 degrees F., for example, but at any event is less than 170 degrees F. Assuming that the thermostat bellows in the thermostatic device 52 is already in the position corresponding to 140 degrees F., for example, the valve head in the valve is not moved and the water passes through the pipe 58, thermostat chamber 6|, valve 89, and pipe 62 to the heater tank ll without change in the impedance of this circuit. However, in the event that the magma in the tank It remains therein for a longer period than that for which the apparatus is adjusted, such, for example, as the result of the stopping of the centrifugal machines, the rate at which heat energy must be supplied to the magma to maintain it at the desired temperature is substantially less than that required to eifect rapid heating, for only as much heat is needed as will offset heat loss from the magma by radiation or otherwise. If, nevertheless, the water entering the coil sections l9 and the coil sections 20 continued at the same volume, it is obvious that the magma would be dangerously overheated. However, the higher the magma temperature, the smaller is the temperature differential between the heating water and the magma, and the lower the rate at which heat is extracted from the water passing through the coil sections IS and 20. In consequence of any reduction in the rate of extraction of heat from the coils, the temperature of the water leaving the coil I 8 tends to rise. In this situation, the thermostat 52 operates the valve 60 in such direction as to increase the impedance presented to the circulation of water by the pump l6 and thereby to reduce the velocity of flow, the volume of hot water entering the coil, and the amount of heat imparted to the magma by the coil. If the magma remains in the tank [0 a shorter than normal period of time, the reverse of the above analysis is true and the valve 60 is operated to decrease the impedance of the circuit and thus to increase the velocity of flow, thereby increasing the volume of the fluid supplied to the inlet of the coil [8. This action has the effect of heating the magma more slowly when it is near the desired temperature and faster when it is much less than this temperature and also of preventing overheating of the magma when the desired temperature is attained.

The system described above makes it possible to determine within very close limits the temperature of the massecuite actually being heated and stirred. As pointed out above, a reading taken within the tank It! does not give an accurate picture of the temperature of the massecuite in contact with the rotating coil it. However, by locating the temperature taking point within the water circulatory system itself,

6 a very accurate reading can be taken by following the method now to be described.

Assume that hot water is running in the circulatory system (the valve 1|] being opened) and that the coil I8 is rotating, thus heating the massecuite M in the tank H]. Experience in the operation of this system tells the operator just about when to note the temperature on the scale [it to see if the massecuite is approaching the desired temperature. At this time, the operator closes the valve 10 (either directly or from the remote station H by compressed air or by electric wires or other suitable means connecting points 10 and 'H) and permits the coil [8 to rotate in the massecuite for a period of from 5 to 15 minutes, depending upon the details of the coil design and the amount of heating surface thereon.

In this period when the water is not circulated, it will obviously continue exchanging heat with the massecuite and thus the water in the coil comes to a temperature very close to that of the massecuite. Therefore at the end of a 5 to 15 minute period, the operator moves the handle or other control at the remote station 1| to open valve 79. This allows the water again to flow into the coil l8 and has the effect of pushing water which has been in the coil out of the latter and in contact with the bulb 63 of the thermometer. This causes the thermometer scale 64 to indicate the temperature of the outfiowing water which is the temperature of the massecuite which has been stirred by the coil, and therefore the reading of the thermometer M is a very close approximation of the actual temperature of the massecuite.

An important advantage of this method of determining the massecuite temperature is that the temperature of the bulk of the massecuite stirred by the coil is obtained and not the temperature of some small unstirred portion. This permits very accurate control of the massecuite temperature because obviously if it is found to be hot enough, i. e. at saturation temperature, the heating process is turned off, but if it is still too cold then the heating can be continued and other observation following the same process can be taken until the actual temperature of the massecuite is the saturation temperature. Obviously, there are many places in the circulatory system into which the thermometer bulb could be placed, either outside or inside the coil. A position inside the center pipe of the rotating coil near the outflow end will give good results.

W hat is claimed is:

l. The method of measuring the temperature of massecuite in a mixing tank which has its temperature varied by heat exchange with a hollow rotating coil through which fluid is adapted to fiow, which comprises the steps of passing fluid through said coil for a first time period, the fluid itself being out of direct contact with said massecuite, cutting off the flow of said fluid through said coil and rotating the coil in said massecuite a second time period long enough so that the fluid trapped in said coil and the massecuite reach substantially the same temperature, removing said trapped fluid from said coil, and measuring the temperature of said trapped fluid after the fluid has passed through at least part of the rotating coil and exchanged heat with the massecuite.

2. The method of measuring the temperature of massecuite in a mixing tank which has its temperature varied by heat exchange with a masseouite, cutting off the flow of said fluid 5 through said coil and rotating the coil in said massecuite a secondtime period long enough so that the fluid trapped in said coil and the masseouite reach substantially the same temperature, removing said trapped fluid from said coil, and measuring the temperature of said trapped fluid outside said coil in a channel which feeds back the trapped fluid into said coil.

References Cited' in the file of this patent UNITED STATES PATENTS Number Name Date 1,917,810 Reynoldson July 11. 1933 2,254,389 olcott Sept. 2', 1941 OTHER REFERENCES Baselt et al. (article), Temperature: Its Measurement and Control in Science and Industry; Reinhold Publishing Company, 330 W. 42nd St, New York, N. Y., 1941; page 870. QC 271.A6. 

